This invention relates to a method for producing a hydrogen occlusion material, and more particularly to a method for producing a material for occluding hydrogen therein.
In order to render hydrogen available as, for example, a power source for an automobile or the like, much effort has been directed to research and development of a hydrogen occlusion material which is capable of efficiently occluding hydrogen therein.
A method for storing hydrogen in a predetermined amount for every one time has been conventionally proposed, which is generally classified into two techniques. One is gaseous hydrogen storage techniques of storing hydrogen in the form of gas and the other is liquefied hydrogen storage techniques of storing liquefied hydrogen rather than gaseous hydrogen. In addition to the above, hydrogen storage techniques of occluding hydrogen in hydrogen occlusion alloy have been also known in the art.
The gaseous hydrogen storage techniques described above require a stout gas bomb of a relatively large volume which acts as a hydrogen storage means. This causes the gas bomb to be large-sized and increased in weight, resulting in the bomb being unsuitable for mounting on a vehicle such as an automobile or the like and inconvenient for shipping and transferring. The liquefied hydrogen storage techniques require to keep a storage section at a temperature as low as xe2x88x92253xc2x0 C. because liquefied hydrogen must be stored in the form of liquid. This causes an apparatus for liquefied hydrogen storage to be significantly large-scaled. Thus, the latter techniques encounter such a disadvantage as in the former techniques and renders the apparatus highly expensive.
The conventional hydrogen occlusion method described above is developed for the reason that it does not encounter the above-described problem as seen in the gaseous or liquefied hydrogen storage techniques and is considered to be a means with a bright future. Hydrogen occlusion alloys used for the method include titanium alloy, magnesium alloy, rare earth alloy, palladium alloy and the like. Unfortunately, the hydrogen occlusion alloys each have a disadvantage of being relatively increased in high hydrogen discharge temperature, resulting in being of no practical use.
Recently, so-called carbon nanotubes have come to notice in the art as a hydrogen occlusion material which exhibits enhanced hydrogen occlusion characteristics (see Nature, 386, pp 377-379, 1997). However, for example, in order to permit an automobile to run by a distance as long as about 500 km, it is required to consume hydrogen in an amount of 3.1 kg. Thus, the carbon nanotubes fail to be put to practical use in view of its hydrogen storage volume and its own weight.
Also, a hydrogen storage method for storing hydrogen in a hydrogen occlusion material which may be mounted in an automobile is proposed, as disclosed in Japanese Patent Application Laid-Open Publication No. 72201/1998. In the publication, platinum metal is applied in the form of a metal film to activated carbon, fullerene, carbon nanotubes or a mixture thereof, so that the platinum metal film dissociates hydrogen molecules into hydrogen atoms. Then, the hydrogen atoms are stored in carbon nanotubes or the like.
In the hydrogen storage method disclosed in the publication, the hydrogen occlusion material is prepared by forming a film of platinum metal on a carbonaceous material such as carbon nanotubes or the like by conventional metal film formation techniques such as vacuum deposition, sputtering, CVD or the like. Thus, the manufacturing of the carbonaceous material such as carbon nanotubes or the like and metal and formation of the metal film are carried out independently from each other, so that the hydrogen storage method is highly complicated because of being increased in the number of steps and requires a large-scaled manufacturing apparatus, leading to an increase in production cost.
The present invention has been made in view of the foregoing disadvantage of the prior art.
Accordingly, it is an object of the present invention to provide a method for producing a hydrogen occlusion material which is capable of producing a hydrogen occlusion material during manufacturing of a carbonaceous material such as carbon nanotubes or the like, to thereby facilitate production of the hydrogen occlusion material at a reduced cost.
In accordance with the present invention, a method for producing a hydrogen occlusion material is provided. In the method, metal which exhibits a catalytic function of dissociating hydrogen molecules into hydrogen atoms is evaporated together with a carbon material to which a metal catalyst for producing a carbonaceous material such as carbon nanotubes or the like is added, resulting in producing the hydrogen occlusion material constituted by the metal and carbonaceous material.
The metal which exhibits the function of hydrogen molecules into hydrogen atoms may be at least one selected from the group consisting of platinum metals, oxide metals of platinum metals and alloys of platinum metals.
The metal catalyst added to the carbon material may be selected from the group consisting of Fe, Co, Ni, Y, Rh, Pd, Pt, Ru, La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Lu and any mixture thereof.
The carbonaceous materials may include single-layer carbon nanotubes.